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G D Calvert

Publications and source records attributed to G D Calvert.

11 recordsLinked to original sources
PubMed1979

Electroimmunoassay of a subunit protein in a macromolecular complex (apolipoprotein B in human plasma very low density lipoprotein); implications for other electroimmunoassay systems.

With an electroimmunoassay ("rocket") system for the apolipoprotein B component of the plasma very low density lipoprotein complex we obtained results which were similar to those obtained by a colorimetric tetramethylurea extraction method. Results were up to twice as high as those using radioimmunoassay. Low density lipoprotein containing apolipoprotein B as the only demonstrable protein component was used as the standard for these assays. This protein produced larger and higher rockets at pH 8.6 when the negative particle charge was increased by maleylation. The very low density lipoprotein complex has a higher negative charge at pH 8.6 than low density lipoprotein. These findings suggest that some apolipoprotein B in vary low density lipoprotein is not "recognised" by anti-apolipoprotein B antibodies, hence radioimmunoassay results are lower than those obtained with the tetramethylurea extraction method. The higher negative charge on very low density lipoprotein particles (compared with low density lipoprotein), as a factor tending to increase rocket area and height, is counterbalanced by reduced recognition by antiapolipoprotein B antibodies. The net result of these opposing tendencies is that the rocket electroimmunoassay of apolipoprotein B in very low density lipoprotein fortuitously gives valid results, under the specified assay conditions. We conclude that electroimmunoassays of complex proteins are not necessarily valid if protein subunits are used for standards. This has implications for the electroimmunoassay of other apolipoproteins.

Apolipoproteins↗
PubMed1979

Rapid cholesterol measurement: patient classification in heart risk evaluation clinics.

Plasma cholesterol levels of patients attending a heart risk evaluation clinic were measured both in the clinic at the time of attendance, and later in a reference laboratory. The workflow of evaluation clinics may be improved, and patient satisfaction enhanced, by in situ measurement, since more than 60% of patients can be given a complete risk score at the time of attendance.

Cholesterol↗
PubMed1979

In vivo metabolism of esterified cholesterol and apoproteins in rabbit plasma low density lipoproteins.

Preparations of rabbit low density lipoproteins (LDL) labelled with 3H in the esterified and free cholesterol moieties and with 125I in the apoprotein moiety were injected intravenously into other rabbits. A substantial proportion of the esterified [3H]cholesterol removed from LDL during the first 30 min was recovered in the high density lipoprotein (HDL) fraction, while no such transfer of labelled apoprotein was observed. There was a clear cut differential in the decay of the different LDL components, slowest for the apoprotein, intermediate for esterified cholesterol and fastest for free cholesterol.

Animals↗
PubMed1978

Effects of therapy on plasma-high-density-lipoprotein-cholesterol concentration in diabetes mellitus.

In 122 diabetic patients there was a signnificant inverse correlation between plasma-high-density-lipoprotein (H.D.L.)-Cholesterol concentrations and glycosylated haemoglobin concentrations. In an insulin-treated subgroup improvement in diabetic control, confirmed by a decrease in glycosylated haemoglobin concentrations, was accompanied by a significant rise in plasma-H.D.L.-cholesterol concentration. This result suggests that improved diabetic control may diminish the risk of premature ischaemic heart-disease. When three groups of patients on different treatments were matched for age, sex, weight, and diabetic control, diabetic patients receiving sulphonylureas had significantly lower plasma-H.D.L.-cholesterol concentrations than those receiving insulin or on diet alone, or non-diabetic controls. This association suggests that sulphonyl-urea administration may constitute a positive risk factor for ischaemic heart-disease in diabetic patients.

Adolescent↗
PubMed1977

The effect of bile salts on the esterolytic assay of trypsin.

A bile salt mixture and pure sodium taurocholate were each shown to increase the esterolytic activity of trypsin in aqueous solution and in intestinal juice. rho-Toluene-sulphonyl-L-arginine methyl ester (TAME) was used as a substrate, and both a spectrophotometric and a potentiometric assay system were used. The maximal potentiation of the esterolytic activity of trypsin by bile salts was about 1.6 to 2.2 times the activity without bile salts (depending on the assay conditions and whether the trypsin was in aqueous solution or intestinal juice). The proteolytic activity of trypsin was decreased by the addition of bile salts. It seemed likely, therefore, that the potentiating effect of bile salts on trypsin esterolytic activity is primarily on the substrate (TAME) rather than trypsin itself. It was thought that TAME might be taken up into bile salt micelles and thus be more readily hydrolysed by trypsin, but we were unable to substantiate this hypothesis. The precision of the trypsin esterolytic assay was better when bile salts were not added. If however bile salts were to be used routinely in the trypsin assay, it would be useful to ensure that the concentration of calcium, included as activator, is sufficiently low to prevent the formation of a precipitate. This precipitate is probably a complex of calcium and bile salts.

Bile Acids and Salts↗
PubMed1977

Percutaneous cardiac puncture in domestic pigs.

Blood sampling by percutaneous cardiac puncture was carried out in 69 domestic pigs. The procedure was shown to be safe and to produce reproducible data. The technique can be carried out without anaesthesia. Repeated sampling is possible over minutes, hours or days, and a wide range of sample volumes can be achieved by this technique.

Animals↗
PubMed1976

Attracting and training more chemical pathologists in the United Kingdom.

I have attempted to define the function of the medical graduate in the clinical biochemistry laboratory and have examined data on recrutiment in the United Kingdom into clinical biochemistry. If trainee pathologists were encouraged to become proficient in both a branch of clinical medicine and in research techniques, the resulting chemical pathologists should be able to improve the consultative and investigative functions of the laboratory. To this end I have suggested some changes in the training regulations and in the role of the chemical pathologists.

Biochemistry↗
PubMedDate not supplied

Properties of two pig low density lipoproteins prepared by zonal ultracentrifugation.

Pig plasma lipoproteins were separted into four density classes (very low density, two low density and high density lipoproteins, VLDL, LDL1, LDL2 and HDL respectively) from 670 ml plasma by ultracentrifugation in a continuous density gradient using the Spinco Ti15 zonal rotor. LDL1 and LDL2 were partly characterised. LDL1 and LDL2 are beta-migrating lipoproteins of different size and hydrated density; they are similar to human LDL2 and LDL3 respectively. Pig plasma contains about twice as much LDL1 as LDL2. LDL1 migrates at Sf 4.9 (modal value), and has a mean diameter of 217 A and a modal density of 1.035 g/ml (range 1.03-1.04 g/ml). LDL2 migrates at Sf 1.8 and has a mean diameter of 195 A and a density of 1.050 g/ml. Both lipoproteins are precipitated by heparin and Mn++ or by dextran sulphate and Ca++. The apoproteins of LDL1 and LDL2 are both largely insoluble in 8 M urea solution. When dissolved in 1% sodium dodecyl sulphate solution and electrophoresed on polyacrylamide gel at pH 7.0, the apoproteins of LDL1 and LDL2 formed a pattern of multiple bands of high molecular weight similar to that obtained from the apoprotein of human LDL. Both LDL1 and LDL2 share a major antigen with each other and with VLDL; in this respect again they resemble human LDL. The amino acid compositions of LDL1 and LDL2 are very similar. We concluded that the apoprotein moieties of pig plasma LDL1 and LDL2 are probably identical, and similar to apoprotein B in human serum. Zonal ultracentifugation has proved to be a rapid and effective method for isolating large quantities of these two lipoprotein classes for further metabolic studies. This method allows rapid bulk preparation of lipoproteins, and provides a record of their distribution and quantity in a continuous density gradient.

Amino Acids↗
PubMedDate not supplied

The plasma and tissue turnover and distribution of two radio-iodine-labelled pig plasma low density lipoproteins.

Two classes of pig plasma low density lipoprotein (LDL1 and LDL2) with different densities and molecular sizes were isolated by zonal ultracentrifugation and were further purified by flotation. The peptide component was iodinated with 125I, and the labelled lipoprotein was injected intravenously. 125I-LDL1 turnover studies were performed on 22 3-4 month old female Large White pigs, and 125I-LDL2 turnover studies on 4 similar pigs. A biological screening experiment confirmed that the shape of the plasma activity curve was not a function of protein denaturation. The pattern of radioactivity decline in plasma was not affected by the degree of LDL iodination. 125I-LDL1 turnover: The curve of plasma radioactivity plotted against time over the first 5 days after injection could be resolved into two exponentials. The plasma biological half-life (T 1/2) was calculated from the slower exponential predominant from the second day. The mean T 1/2 over 2-5 days was 22.9 hr (range 17.2-28.5 hr). Multicompartmental analysis of the plasma decay curve using an open mammillary model gave a mean fractional catabolic rate per day for LDL1 of 1.4 (range 0.9-1.9). The mean T 1/2 was 0.26-0.31 times and the fractional catabolic rate 3.0-3.9 times those values found in two studies on adult humans. The tissue distribution of 125I was analysed in a series of 20 animals killed from 1.0 to 33.8 days after 125I-LDL1 injection. Most tissue 125I (86-89%) was protein bound. An appropriate correction was made to the 125I counts for retained plasma in liver and spleen (using 131I-albumin); retained plasma in other tissues was negligible. Highest 125I tissue levels were found in the liver, supporting other evidence that the liver may be the major site of LDL1 catabolism. After 2.06 and 4.06 days the livers in two animals contained 1.6% and 0.7% respectively of the total injected 125I, equal to 33% and 54% of the total plasma 125I at those times. The skin contained about one-third to one-ninth the 125I in the liver at various times. Distribution in other organs was quantitatively minimal. Higher levels of radioactivity were found in the intima and inner media of the aorta than in the outer media. These results suggest that plasma LDL in the pig diffuses through the endothelial surface into the arterial wall. These findings are confirmed by autoradiography. 125I-LDL2 turnover: Parallel studies of plasma 125I-LDL2 turnover and tissue distribution were performed. The plasma biological decay curve was multi-exponential, suggesting that LDL2 metabolism is complex, and possibly more rapid than that of LDL1 (LDL2 is smaller and denser than LDL1). The tissue distribution of 125I-LDL2 in these pigs was very similar to that of 125I-LDL1. As LDL1 and LDL2 differ in the amount of lipid they contain, they may have different roles to play in lipid transport, and there may be interconversion of one into the other at different sites. This hypothesis remains conjectural.

Animals↗